Screening calls feature or bug???

Ok so I thought I was hearing things the first time this happend, but before I answered an incoming call on my evo I heard a voice on the other end while my phone was ringing. Well today I heard it again so I decided to check it out, so I called myself on my girlfriends phone and lo and behold I could hear myself on my evo while it was ringing before I even touched the slide to unlock.

I searched around to see if this was a known feature or bug, but I haven't seen a thing, anyone else notice this?????? Its pretty cool to have lol.

Well it happens even before I pick the phone up off the table, but this seems to be some kind of bug or glitch because its intermittent, I got my dad to call me (he's on sprint) and it didn't do it, the other 2 phones that it did work on were on att and verizon but I tried a couple of more times they did it about 3 out of 5 times so its frequent but not consistent.